From f8373c1f19fa2ba3ebde7ff272860a3931016a2b Mon Sep 17 00:00:00 2001
From: Kasper Svendsen <kaspersv@github.com>
Date: Thu, 9 Jan 2025 09:35:56 +0100
Subject: [PATCH] Define entity discard predicates for Java

---
 java/ql/lib/java.qll                       |  1 +
 java/ql/lib/semmle/code/Location.qll       | 14 +++++++++
 java/ql/lib/semmle/code/java/Expr.qll      | 13 +++++++++
 java/ql/lib/semmle/code/java/Javadoc.qll   | 13 +++++++++
 java/ql/lib/semmle/code/java/Member.qll    | 33 ++++++++++++++++++++++
 java/ql/lib/semmle/code/java/Overlay.qll   | 29 +++++++++++++++++++
 java/ql/lib/semmle/code/java/Statement.qll | 13 +++++++++
 java/ql/lib/semmle/code/java/Variable.qll  | 13 +++++++++
 8 files changed, 129 insertions(+)
 create mode 100644 java/ql/lib/semmle/code/java/Overlay.qll

diff --git a/java/ql/lib/java.qll b/java/ql/lib/java.qll
index 9644343e93b..82c37282379 100644
--- a/java/ql/lib/java.qll
+++ b/java/ql/lib/java.qll
@@ -26,6 +26,7 @@ import semmle.code.java.KotlinType
 import semmle.code.java.Member
 import semmle.code.java.Modifier
 import semmle.code.java.Modules
+import semmle.code.java.Overlay
 import semmle.code.java.Package
 import semmle.code.java.Statement
 import semmle.code.java.Type
diff --git a/java/ql/lib/semmle/code/Location.qll b/java/ql/lib/semmle/code/Location.qll
index 14fc7a99532..cd5b41ca749 100644
--- a/java/ql/lib/semmle/code/Location.qll
+++ b/java/ql/lib/semmle/code/Location.qll
@@ -221,3 +221,17 @@ private predicate fixedHasLocation(Top l, Location loc, File f) {
   not hasSourceLocation(l, _, _) and
   locations_default(loc, f, _, _, _, _)
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableLocation(string file, @location l) {
+  not hasOverlay() and
+  file = getRawFileForLoc(l) and
+  not exists(@file f | hasLocation(f, l))
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardLocation(@location l) {
+  exists(string file | discardableLocation(file, l) and discardFile(file))
+}
diff --git a/java/ql/lib/semmle/code/java/Expr.qll b/java/ql/lib/semmle/code/java/Expr.qll
index 182bf5b7001..814da6ce1c8 100644
--- a/java/ql/lib/semmle/code/java/Expr.qll
+++ b/java/ql/lib/semmle/code/java/Expr.qll
@@ -2701,3 +2701,16 @@ class RecordPatternExpr extends Expr, @recordpatternexpr {
     )
   }
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableExpr(string file, @expr e) {
+  not hasOverlay() and
+  file = getRawFile(e)
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardExpr(@expr e) {
+  exists(string file | discardableExpr(file, e) and discardFile(file))
+}
diff --git a/java/ql/lib/semmle/code/java/Javadoc.qll b/java/ql/lib/semmle/code/java/Javadoc.qll
index ef8f77bf9ba..f9132e7ad05 100644
--- a/java/ql/lib/semmle/code/java/Javadoc.qll
+++ b/java/ql/lib/semmle/code/java/Javadoc.qll
@@ -196,3 +196,16 @@ class KtCommentSection extends @ktcommentsection {
   /** Gets the string representation of this section. */
   string toString() { result = this.getContent() }
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableJavadoc(string file, @javadoc d) {
+  not hasOverlay() and
+  exists(@member m | file = getRawFile(m) and hasJavadoc(m, d))
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardJavadoc(@javadoc d) {
+  exists(string file | discardableJavadoc(file, d) and discardFile(file))
+}
diff --git a/java/ql/lib/semmle/code/java/Member.qll b/java/ql/lib/semmle/code/java/Member.qll
index 662eab06bd1..e3ea0605e1f 100644
--- a/java/ql/lib/semmle/code/java/Member.qll
+++ b/java/ql/lib/semmle/code/java/Member.qll
@@ -897,3 +897,36 @@ class ExtensionMethod extends Method {
     else result = 0
   }
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableMethod(string file, @method m) {
+  not hasOverlay() and
+  file = getRawFile(m) and
+  exists(@classorinterface c | methods(m, _, _, _, c, _) and isAnonymClass(c, _))
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardAnonMethod(@method m) {
+  exists(string file | discardableMethod(file, m) and discardFile(file))
+}
+
+overlay[local]
+pragma[nomagic]
+predicate discardableBaseMethod(string file, @method m) {
+  not hasOverlay() and
+  file = getRawFile(m)
+}
+
+overlay[local]
+pragma[nomagic]
+predicate usedOverlayMethod(@method m) { hasOverlay() and methods(m, _, _, _, _, _) }
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardMethod(@method m) {
+  exists(string file |
+    discardableBaseMethod(file, m) and discardFile(file) and not usedOverlayMethod(m)
+  )
+}
diff --git a/java/ql/lib/semmle/code/java/Overlay.qll b/java/ql/lib/semmle/code/java/Overlay.qll
new file mode 100644
index 00000000000..caeb2f0ddee
--- /dev/null
+++ b/java/ql/lib/semmle/code/java/Overlay.qll
@@ -0,0 +1,29 @@
+overlay[local?]
+module;
+
+import java
+
+overlay[local]
+pragma[nomagic]
+predicate hasOverlay() { databaseMetadata("isOverlay", "true") }
+
+overlay[local]
+string getRawFile(@locatable el) {
+  exists(@location loc, @file file |
+    hasLocation(el, loc) and
+    locations_default(loc, file, _, _, _, _) and
+    files(file, result)
+  )
+}
+
+overlay[local]
+string getRawFileForLoc(@location l) {
+  exists(@file f | locations_default(l, f, _, _, _, _) and files(f, result))
+}
+
+overlay[local]
+pragma[nomagic]
+predicate discardFile(string file) {
+  hasOverlay() and
+  exists(@expr e | callableEnclosingExpr(e, _) and file = getRawFile(e))
+}
diff --git a/java/ql/lib/semmle/code/java/Statement.qll b/java/ql/lib/semmle/code/java/Statement.qll
index 73b0aac5cbd..0591155037f 100644
--- a/java/ql/lib/semmle/code/java/Statement.qll
+++ b/java/ql/lib/semmle/code/java/Statement.qll
@@ -987,3 +987,16 @@ class SuperConstructorInvocationStmt extends Stmt, ConstructorCall, @superconstr
 
   override string getAPrimaryQlClass() { result = "SuperConstructorInvocationStmt" }
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableStmt(string file, @stmt s) {
+  not hasOverlay() and
+  file = getRawFile(s)
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardStmt(@stmt s) {
+  exists(string file | discardableStmt(file, s) and discardFile(file))
+}
diff --git a/java/ql/lib/semmle/code/java/Variable.qll b/java/ql/lib/semmle/code/java/Variable.qll
index 50fd7a06484..875c39d8443 100644
--- a/java/ql/lib/semmle/code/java/Variable.qll
+++ b/java/ql/lib/semmle/code/java/Variable.qll
@@ -133,3 +133,16 @@ class Parameter extends Element, @param, LocalScopeVariable {
   /** Holds if this is an anonymous parameter, `_` */
   predicate isAnonymous() { this.getName() = "" }
 }
+
+overlay[local]
+pragma[nomagic]
+predicate discardableLocalVarDecl(string file, @localscopevariable l) {
+  not hasOverlay() and
+  file = getRawFile(l)
+}
+
+overlay[discard_entity]
+pragma[nomagic]
+predicate discardLocalVarDecl(@localscopevariable l) {
+  exists(string file | discardableLocalVarDecl(file, l) and discardFile(file))
+}